This application relates to an all-reflective optical imaging system and, more particularly, to such a system which permits changing the field of view while maintaining the pupil location of the imaging system.
An optical imaging system typically includes optical components that focus an incident optical beam to a sensing device at a focal plane. A sensor, image recording device, or other component is located at the focal plane to utilize the focused optical beam. The imaging system may be required to be operable at a single wavelength or in a narrow wavelength range, and either reflective or refractive optics may be used.
The imaging system may instead be required to be operable over a wide range of wavelengths such as, for example, both visible and infrared wavelength ranges. In that case, refractive optics generally cannot be used, because the lenses have wavelength-dependent focal lengths and aberrations. The focal plane location of a refractive imaging system varies as a function of the wavelength of the radiation, complicating or degrading the imaging process. Accordingly, all-reflective imaging systems are preferred for these wide-band applications, because the focal length and aberrations of a mirror system are independent of the wavelength of the incident radiation.
Another requirement of some optical imaging systems is the ability to change the field of view between two or more fields (termed "field-switching"), such as a lower-magnification, wider-angle view, and a higher-magnification, narrower-angle view. For example, some sensor systems perform initial acquisition scans with the wide-angle view, and then switch to the narrow-angle view once a target has been located.
Field-switching optical imaging devices are widely available for refractive systems, zoom lenses being a common example. In these devices, lenses or groups of lenses are moved relative to each other to effect the field switching. However, structures to achieve comparable results for all-reflective optical imaging devices are not available. There is, accordingly, a need for an all-reflective optical imaging system with field-switching capability and which maintains the pupil location fixed as the field of view changes. The present invention fulfills this need, and further provides related advantages.